Hey there,
I think that could be a great idea.
As long as you've already done the datacron once, it could be useful and smart to permit an unlocking : "spread it to all your alts". Datacron requires time, skil and concentration, and when you success once, you're rewarded that for (time/concentration). Why should we be granted several times for a single skill mastery?
In my opinion, Cartel Coins will obviously be a normal way to get it, as it'll provide a little advantage in high level gaming experience.
About the double skill tree, each MMO I've been playing in have it, and it is a huge timesaver!
+2 then,
/signed
PS : please excuse me for my poor english, comming from FR server